Secreted Protein, Acidic, Rich in Cysteines (SPARC), also known as osteonectin, is a 281 amino acid glycoprotein. SPARC has affinity for a wide variety of ligands including cations (e.g., Ca2+, Cu2+, Fe2+), growth factors (e.g., platelet derived growth factor (PDGF), and vascular endothelial growth factor (VEGF)), extracellular matrix (ECM) proteins (e.g., collagen I-V and collagen IX, vitronectin, and thrombospondin-1), endothelial cells, platelets, albumin, and hydroxyapaptite. SPARC expression is developmentally regulated, and is predominantly expressed in tissues undergoing remodeling during normal development or in response to injury (see, e.g., Lane et al., FASEB J., 8, 163-173 (1994)). High levels of SPARC protein are expressed in developing bones and teeth.
SPARC is a matricellular protein upregulated in several aggressive cancers, but is absent from the vast majority of normal tissues (Porter et al., J. Histochem. Cytochem., 43, 791 (1995) and see below). Indeed, SPARC expression is induced among a variety of tumors (e.g., bladder, liver, ovary, kidney, gut, and breast). In bladder cancer, for example, SPARC expression has been associated with advanced carcinoma. Invasive bladder tumors of stage T2 or greater have been shown to express higher levels of SPARC than bladder tumors of stage T1 (or less superficial tumors), and have poorer prognosis (see, e.g., Yamanaka et al., J. Urology, 166, 2495-2499 (2001)). In meningiomas, SPARC expression has been associated with invasive tumors only (see, e.g., Rempel et al., Clinical Cancer Res., 5, 237-241 (1999)). SPARC expression also has been detected in 74.5% of in situ invasive breast carcinoma lesions (see, e.g., Bellahcene, et al., Am. J. Pathol., 146, 95-100 (1995)), and 54.2% of infiltrating ductal carcinoma of the breast (see, e.g., Kim et al., J. Korean Med. Sci., 13, 652-657 (1998)). SPARC expression also has been associated with frequent microcalcification in breast cancer (see, e.g., Bellahcene et al., supra), suggesting that SPARC expression may be responsible for the affinity of breast metastases for the bone. SPARC is also known to bind albumin (see, e.g., Schnitzer, J. Biol. Chem., 269, 6072 (1994)).
Albumin nanoparticle formulations have been shown to reduce toxicity of poorly soluble therapeutic agents. For example, U.S. Pat. No. 6,537,579 discloses an albumin-nanoparticle paclitaxel formulation which is free of toxic emulsifiers.
The anticancer agent paclitaxel, marketed under the trademark Taxol® by Bristol Myers Squibb, is currently approved for the treatment of several cancers including ovarian, lung, and breast cancer. A major limitation to the use of paclitaxel is its poor solubility. Consequently, the Taxol® formulation contains Cremophor® EL as the solubilizing vehicle, but the presence of Cremophor® in this formulation has been linked to severe hypersensitivity reactions in animals (Lorenz et al., Agents Actions 7, 63-67, 1987), and humans (Weiss et al., J. Clin. Oncol. 8, 1263-1268, 1990). Accordingly, patients receiving Taxol® require premedication with corticosteroids (dexamethasone) and antihistamines to reduce the hypersensitivity and anaphylaxis that occurs due to the presence of Cremophor®.
In contrast, Abraxane®, also known as ABI-007, is a Cremophor®-free, albumin-nanoparticle formulation of paclitaxel, marketed by Abraxis Oncology. The use of an albumin nanoparticle as a vehicle results in the formation of a colloid when reconstituted with saline. Based on clinical studies, it has been shown that the use of Abraxane® is characterized by reduced hypersensitivity reactions as compared with Taxol®. Accordingly, premedication is not required for patients receiving Abraxane®.
Another advantage of the albumin-nanoparticle formulation is that by excluding toxic emulsifiers it is possible to administer higher doses of paclitaxel at more frequent intervals than is currently possible with Taxol®. The potential exists that enhanced efficacy could be seen in solid tumors as a consequence of (i) higher tolerable doses (300 mg/m2), (ii) longer half-life, (iii) prolonged local tumor availability and/or (iv) sustained in vivo release. Abraxane® reduces hypersensitivity reactions while maintaining or improving the chemotherapeutic effect of the drug.
It is known that colloidal nanoparticles or particles <200 nm in size tend to concentrate at the tumor site due to leaky vasculatures. This effect has been described for several lipsomal formulations (Papahadjopoulos, et al., Proc. Natl. Acad. Sci. U.S.A. 88, 11460, 1991); (Gabizon, A., Cancer Res., 52, 891, 1992); (Dvorak, et al., Am. J. Pathol. 133, 95, 1988); (Dunn, et al., Pharm, Res., 11, 1016-1022, 1994); and (Gref, et al, Science 263, 1600-1603, 1994). It is possible that localized nanoparticles of paclitaxel at the tumor site may result in slow release of the drug at the tumor site resulting in greater efficacy when compared to administration of the drug in its solubilized (Cremophor®-containing) form.
Such nanoparticle formulations comprise at least about 50% of the active agent in nanoparticle form. Further, such nanoparticle formulations comprise at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the active agent in nanoparticle form. Moreover, such nanoparticle formulations comprise at least about 95% or at least about 98% of the active agent in nanoparticle form.
Antibody therapy is an effective method for controlling disease wherein a specific protein marker can be identified. Examples include Avastin—an anti-VEGF antibody, Rituxan—an anti-CD20 antibody, and Remicade—an anti-TNF antibody. As such, an antibody against SPARC would represent an important therapeutic agent for treating human and other mammalian tumors, as well as other proliferative, hyperplastic, remodeling, and inflammatory disorders that express the SPARC protein. In addition, an antibody against SPARC conjugated with an imaging or contrast agent would be a means of detecting and diagnosing such disorders.
There remains a need for a method of predicting the responsiveness of human and other mammalian tumors, as well as other proliferative, hyperplastic, remodeling, and inflammatory disorders, to specific therapies. There also remains a need for a method of treating human and other mammalian tumors, as well as other proliferative, hyperplastic, remodeling, and inflammatory disorders. Moreover, there remains a need for predicting or determining the response of a human or other mammalian tumor in order to predict or evaluate the effectiveness of the chemotherapeutic agent or other anti-cancer therapy. In addition, suitable means are needed in order to detect and diagnose such disorders. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.